The Constitution provides for a president pro tempore to preside over the Senate in the absence of the vice president. Except for the years from 1886 to 1947, the president pro tempore has been included in the presidential line of succession. Following passage of the Presidential Succession Act of 1792, the president pro tempore was next in line after the vice president, and followed by the speaker of the House of Representatives. In 1886 a new law removed the president pro tempore and the speaker from the line of succession, substituting cabinet officers. A 1947 law changed the order of succession to place the Speaker of the House in line after the vice president, followed by the president pro tempore, and then the secretary of state and other cabinet officers in order of their departments' creation. This is the system in effect today.

Before 1890, the Senate elected a president pro tempore only for the period when the vice president would be absent. Since 1890, the president pro tempore has held office continuously until the election of a successor. The president pro tempore designates other senators to preside in his absence, generally new members of the majority party.

Constitutional Authority

The Constitution provides for two officers to preside over the Senate. The Vice President of the United States is designated as the president of the Senate. In this capacity, the vice president was expected to preside at regular sessions of the Senate, casting votes only to break ties. From John Adams in 1789 to Richard Nixon in the 1950s, presiding over the Senate was the chief function of vice presidents, who had an office in the Capitol, received their staff support and office expenses through the legislative appropriations, and rarely were invited to participate in cabinet meetings or other executive activities. In 1961, Vice President Lyndon B. Johnson changed the vice presidency by moving his chief office from the Capitol to the White House, by directing his attention to executive functions, and by attending Senate sessions only at critical times when his vote, or ruling from the chair, might be necessary. Vice presidents since Johnson’s time have followed his example.

When we consider that the vice president used to be the Senate's regular presiding officer, we can better understand why the Constitution further provided that in the absence of the vice president the Senate could choose a president pro tempore to perform the duties of the chair. Pro tempore is a Latin term meaning "for the time being"; thus, the occupant of the position was conceived as a temporary presiding officer. Since vice presidents presided routinely in the 18th and 19th centuries, the Senate thought it necessary to choose a president pro tempore only for the limited periods when the vice president might be ill or otherwise absent. As a result, the Senate frequently elected several presidents pro tempore during a single session.

The Constitution is quite unspecific in its definition of the vice president's role as presiding officer, beyond casting tie-breaking votes. John Adams, the first vice president, attempted to influence the Senate’s decisions on legislation during his first term, but eventually came to see the presiding officer as a neutral figure. That role has remained constant since that time. Adams cast more tie-breaking votes (29) than has any vice president who succeeded him. By contrast, during his eight years of service as vice president, George H.W. Bush cast only eight tie-breaking votes, Al Gore broke four ties, and Vice President Dick Cheney voted eight times to break ties. The vice president is not at liberty to address the Senate, except by unanimous consent. Nor should any senator speak while presiding, other than to make necessary rulings and announcements or to maintain order.

Unlike the vice president, the president pro tempore is a duly elected member of the Senate, able to speak and vote on any issue. In the early years, the Senate elected presidents pro tempore on a temporary basis, chosen for their personal characteristics, popularity, and reliability. Since the mid-20th century, it has been traditional for the Senate to elect the senior member of the majority party as president pro tempore.

Presidential Succession

The importance of the post of president pro tempore can be seen by its placement in the presidential line of succession. According to the Presidential Succession Act of 1792, should the offices of president and vice president both become vacant, the president pro tempore would have succeeded to the presidency, followed by the Speaker of the House. This line of succession remained in effect until 1886. The arrangement created a serious consequence on at least one occasion. When President Abraham Lincoln was assassinated in 1865, Vice President Andrew Johnson succeeded to the presidency. When Johnson was impeached in 1868, President pro tempore Benjamin Wade of Ohio stood to gain from conviction. Had the Senate voted to convict and remove Johnson from office (it fell one vote short of the necessary 2/3 majority to convict), Senator Wade would have become president of the United States. Senator Wade, it should be noted, cast his vote in favor of conviction, and President Johnson, after his acquittal, objected to placing the president pro tempore in the line of succession because he would therefore be "interested in producing a vacancy."

Vacancies in the office presented a most pressing problem. In the 18th and 19th centuries, the Senate assumed that it was empowered to elect a president pro tempore only during the absence of a vice president. What should senators do at the end of a session? Since Congress was customarily out of session for half of each year, what would happen if there were no designated president pro tempore? If the vice president died or became president, who would preside at the opening of the next Senate session? Rather than settle these problems by statute or rules changes, the Senate for decades relied upon an elaborate scheme in which the vice president would voluntarily absent himself from the chamber at the end of the session to enable the Senate to elect a president pro tempore, who would then be available to preside if necessary when the Senate reconvened. Some vice presidents refused to perform this little courtesy.

In 1886 Senator George F. Hoar of Massachusetts expressed concern about the frequency of vacancies in the vice presidency and the office of president pro tempore. He called for a revision of the succession act. "The present arrangement is bad," he told the Senate, because "during a large portion of the term there is no officer in being who can succeed." Senator Hoar argued that the Senate did not elect its presidents pro tempore based on any consideration of their fitness to become chief executive. The president pro tempore was by then a senior senator, chosen "for his capacity as a debater and a framer of legislation." Most likely, the president pro tempore would have "little or no executive experience." Hoar then pointed out that no president pro tempore had ever served as president, and only one had even been a candidate for president. By contrast, six secretaries of state had been elected president. Following Hoar's reasoning, Congress in 1886 passed a new law that removed the president pro tempore and Speaker of the House entirely from the line of presidential succession, leaving at its head the secretary of state and the other cabinet members, all non-elected officials.

This remained the order of succession until 1947, when, at the urging of President Harry S. Truman, the law was again revised. Having served ten years in the Senate, Truman held the post of vice president only eighty-two days before Franklin Roosevelt's death propelled him into the White House. As a student of history and a fervent democrat, Truman was troubled that the next person in the line of succession was his secretary of state, Edward Stettinius. The secretary had never run for elective office. As Truman stated, "it was my feeling that any man who stepped into the presidency should have held at least some office to which he had been elected by a vote of the people." Two months after becoming president, Truman proposed restoring the president pro tempore and Speaker of the House to the line of succession.

An interesting feature of Truman's proposal was its reversal of the earlier order of succession, putting the Speaker of the House ahead of the president pro tempore. There were several reasons for this change. In his memoirs, Truman argued that the House Speaker, as an elected representative of his district, as well as the chosen leader of the "elected representatives of the people," should stand next in line to the vice president. Of course, one could make the same argument for the president pro tempore, as the elected official of the people of his state and of the United States Senate. It is likely that specific personalities also played a role in Truman's thinking.

There may also have been an institutional factor in Truman's reversal of the roles. Between the 1886 removal of the president pro tempore from the order of succession and 1947, some entirely new leadership posts had evolved in the Senate: the majority and minority leaders and the party whips. Beginning in the 1920s, when the Democratic and Republican parties first officially designated floor leaders, a number of influential men had been elected majority leader. By 1945, most Washington observers regarded the majority leader as the Senate's functional equivalent of the Speaker of the House of Representatives, while the president pro tempore had become more of a ceremonial office. Had Truman drawn a list of men, rather than offices, he would certainly have included Majority Leader Alben Barkley in the line of succession—indeed, in 1948, Truman chose Senator Barkley as his vice-presidential running mate. For the purposes of legislation, however, the president recommended inclusion of a constitutionally created officer, the president pro tempore, rather than a party-designated officer, the majority leader. Today, the president pro tempore continues to follow the Speaker of the House in presidential succession, followed in turn by the secretary of state and the other cabinet secretaries in the order of their agencies' creation.

Role in the Senate

With regard to the president pro tempore's role in the Senate, an even more significant change took place in 1890, when the Senate agreed that, thereafter, presidents pro tempore would be elected not just for the period of the vice president's absence, but would hold the office continuously until the election of another president pro tempore. As a result, since 1890, with a single exception, each president pro tempore has served until he retired, died, or had the misfortune to see his party lose its majority.

The first sentence of Rule I of today's standing rules of the Senate provides that the president pro tempore shall hold the office "during the pleasure of the Senate and until another is elected or his term of office as a Senator expires." The so-called powers of the president pro tempore, which have generally been more responsibilities than powers, have changed a good deal over the past two centuries. Since 1816, presidents pro tempore have received a larger salary than other senators, and, for a period after 1856, they were compensated at the same rate as the vice president. Since March 1969, the salary of the president pro tempore has been the same as that of the majority and minority leaders. For a period in the early 19th century, presidents pro tempore appointed members of the Senate's standing committees, either indirectly or directly. Since 1820, the president pro tempore has had the power to name other senators to perform the duties of the chair in his absence. In modern times, presidents pro tempore have tended to ask new members of the majority party to preside over the Senate, a practice which enables freshmen senators to grow more accustomed to the Senate's rules and procedures.

When the Democratic side is in the majority, the president pro tempore is an ex-officio member of his party's leadership, including the party conference or caucus, the policy committee, and the steering committee, working closely with the majority leader. Under Republican majority, the president pro tempore is an ex-officio member of the Republican Policy Committee. Various laws assign the president pro tempore authority to make appointments to an assortment of national commissions, usually with the advice of the majority leader. If there are minority appointments, the president pro tempore generally acts upon the recommendations of the minority leader in appointing individuals acceptable to the minority. In the absence of the vice president, the president pro tempore may administer all oaths required by the Constitution, may sign legislation, and may fulfill all other obligations of the presiding officer. Unlike the vice president, however, the president pro tempore cannot vote to break a tie vote in the Senate. Also, in the absence of the vice president, the president pro tempore jointly presides with the Speaker of the House when the two houses sit together in joint sessions or joint meetings.

Election of a senator to the office of president pro tempore has always been considered one of the highest honors offered to a senator by the Senate as a body. That honor has been bestowed upon a colorful and significant group of senators during the past two centuries—men who stamped their imprint on the office and on their times.

1 Gaillard was elected after the death of Vice President Elbridge Gerry and continued to serve throughout the Fourteenth Congress, as there was no vice president.

2 Ambrose H. Sevier was not elected as president pro tempore in an official manner, but "permitted to occupy the chair for the day."

3 In March, 1890, the Senate adopted a resolution stating that presidents pro tempore would hold office continuously until the election of another president pro tempore, rather than being elected for the period in which the vice president was absent. With the exception of the unusual case of the 62nd Congress, this new system has continued to the present.

4 William Frye resigned as president pro tempore due to ill health and died on August 8, 1911. Electing his successor proved difficult for the Senate, since Senate Republicans, then in the majority, split between the progressive and the conservative factions, each promoting its own candidate. Likewise, the Democrats proposed their own candidate. As a result of this three-way split, no individual received a majority vote. During May and June of 1911, ballot after ballot failed to elect a president pro tempore. Finally, desperate to return to regular business, senators agreed to a compromised solution: Democrat Augustus Bacon would serve for a single day, August 14, 1911, during the vice president's absence. Thereafter, Bacon and four Republicans--Charles Curtis, Jacob Gallinger, Henry Cabot Lodge, and Frank Brandegee--would alternate as president pro tempore for the remainder of the 62nd Congress.

5 From January 3 to January 20, 2001 the Democrats held the majority, due to the deciding vote of outgoing Democratic Vice President Al Gore. Senator Robert C. Byrd became the president pro tempore at that time. Starting January 20, 2001, the incoming Republican Vice President Richard Cheney held the deciding vote, giving the majority to the Republicans. Senator Strom Thurmond resumed his role as president pro tempore. On May 24, 2001, Senator James Jeffords of Vermont announced his switch from Republican to Independent status, effective June 6, 2001. Jeffords announced that he would caucus with the Democrats, changing control of the evenly divided Senate from the Republicans to the Democrats. On June 6, 2001, Robert C. Byrd once again became the president pro tempore. On that day, the Senate adopted S. Res. 103, designating Senator Thurmond as President Pro Tempore Emeritus.